It's bad news for princesses, of course, but for empires and armies, poison can be a game-changer.

1. AMERICA’S LETHAL COCKTAIL PARTY

By the mid-1920s, the American government was at its wit’s end. The era’s strict Prohibition laws had proved futile. Americans were still drinking; they were just doing so on the sly, frequenting speakeasies and buying alcohol from crime syndicates. Gangs would steal large quantities of industrial alcohol—used for everything from fueling machines to sterilizing instruments—then redistill the hooch to remove impurities before putting it on the market. In its effort to fight back, the Bureau of Prohibition came up with a shocking idea: What if it poisoned the industrial alcohol supply?

In 1926, the federal government bought into the idea, issuing regulations that required manufacturers to make industrial alcohol more lethal. The new formulas included mercury salts, benzene, and kerosene, and the results were chilling. Alcohol-related deaths skyrocketed, with officials attributing more than a thousand deaths to the program in its first year alone. People were outraged. “The United States government must be charged with the moral responsibility for the deaths,” said New York City medical examiner Charles Norris, one of the measure’s most outspoken foes.

The government held firm on its position even as the body count rose. In New York City, 400 people died the first year. Seven hundred died the next, and the pattern was replicated in cities across the country. Yet Prohibitionists continued to defend the law. The Anti-Saloon League, Norris’s frequent sparring partner, fired back: “Dr. Norris should logically next demand palatable varnish and potable shellac.” Nebraska’s Omaha Bee asked, “Must Uncle Sam guarantee safety for souses?”

It took more than 10,000 American deaths and a furious public backlash for the government to quietly end its “chemists’ war.” But it wasn’t until sometime around 1933, when the regulations were phased out quietly, that what Norris had dubbed “our national experiment in extermination” was officially over.

2. WHERE THERE’S SMOKE, THERE’S FIRE

It should have been a perfect murder. In 1850, Count Hyppolyte de Bocarmé and his wife, Countess Lydie, had a plan to kill her brother for his money. Their weapon: nicotine. But the plan was more involved than providing him with smokes and hoping he’d get emphysema; nicotine, it turns out, is a spectacularly lethal plant alkaloid. Ingesting as little as 30 milligrams of pure nicotine will kill an adult. And for murder, the drug was just the right poison for its time—mid-19th-century scientists had no idea how to detect plant poisons in corpses.

Working from his estate in southern Belgium, the count converted an old laundry into a lab, where he claimed to be mixing up perfumes. In actuality, he was extracting nicotine from tobacco leaves. When the countess’s wealthy brother came to visit, the count and his wife served up a poisoned dinner and attributed his death to stroke. But the servants, unnerved by the count’s strange lab experiments, sensed that something was amiss. They contacted the police, who in turn contacted Jean Servais Stas, Belgium’s best chemist.

Stas, whose work on atomic weights was essential to the creation of the periodic table, relished the challenge. He spent three months searching for a way to extract nicotine from dead tissue. Finally, he found an exact mixture of acids and solvents to detect the lethal compound. The damning results sealed the case, and the count was sentenced to the guillotine. The countess, claiming she’d been forced to participate, escaped charges. Today, the murderous couple is long forgotten, but the crime they committed is remembered for changing forensics—and ending nicotine’s run as the perfect murder weapon.

3. A HONEY OF A WEAPON

Pompey the Great’s soldiers were bone tired. For most of 65 BCE, Roman legions marched around the southern edge of the Black Sea as they battled the local ruler, Mithridates VI of Pontus. Then, something magical happened: The exhausted troops discovered a stockpile of honeycombs strewn across their path, and they fell upon the sticky treats like hungry bears.

But the local honey packed a toxic punch. Within a few hours, the troops began staggering blindly and falling to the ground. Mithridates’s supporters, who had planted the honeycombs along the soldiers’ route, promptly appeared and massacred their incapacitated enemies. Pompey lost three squadrons in the skirmish, a defeat he could have avoided had he brushed up on the region’s military history. In a book published almost 400 years earlier, the Greek general Xenophon reported that his men, after feasting on the region’s wild honey, “all went for the nonce quite off their heads.”

It wasn’t until centuries later, in 1891, that scientists discovered the cause of “mad honey”: rhododendrons. Bees feeding upon the blossoms take in not only nectar but also a grayanotoxin, a poison that disrupts the signaling ability of nerve cells. The symptoms—nausea, headache, dizziness, loss of muscle control, and unconsciousness—can resemble alcohol poisoning. But Mithridates didn’t need to know how it worked to use the honey as a weapon. His soldiers won the battle, delaying (though not preventing) the eventual takeover. As for the Romans, they never made that particular mistake again. Decades later, the writer Pliny the Elder was still warning of the “pernicious” qualities associated with the Black Sea’s golden honey.

4. THE HEAVY METAL THAT ROCKED AN EMPIRE

Modern cooks could probably find their way around a Roman culina. The kitchens featured an oven of sorts and pots and pans made of metal. One major difference, however: Those utensils packed plenty of lead. Soft, flexible, and wonderfully ubiquitous, lead was used to make Roman pipes, coins, and wine jugs. It was even used in face powders and paints. As historian Jack Lewis notes in EPA Journal, the Romans “thought nothing of washing down platters of lead-seasoned food with gallons of lead-adulterated wine.” The result “was the death by slow poisoning of the greatest empire the world has ever known.”

According to one study, two thirds of Roman emperors—from Caligula to Nero—showed symptoms of lead poisoning. Another analysis of bones from Roman cemeteries uncovered lead deposits that measured three times the World Health Organization’s standard for severe lead poisoning.

From top to bottom, lead is bad news for the human body: It damages the kidneys and heart, it impairs the production of red blood cells, and it inhibits the growth of bone cells. But it’s also a neurotoxin, disrupting cognitive processing and affecting the regulation of brain cell growth so severely that synapses often fail to form.

As a result, some historians believe that the poison eventually compromised not just the brains of Roman emperors but everyone in Rome. Suddenly, Caligula declaring his own divinity, appointing his horse to the Senate, and ordering his soldiers into the ocean to “fight the sea god” makes a little more sense.

This story originally appeared in mental_floss magazine. Subscribe to our print edition here, and our iPad edition here.